E守恒定律.ppt

§ §1 1 Impulse Momentum theorem Impulse Momentum theorem §2 The law of Conservation of momentum Chapter 3 The Conservation laws of momentum and Energy §3 Work Energy ic energy theorem §6 Application §5 Collision §4 Potential energy The law of conservation of mechanical Energy § §1 1 Impulse Momentum theorem Impulse Momentum theorem The Newton ’ s law t pt mamFd dd d ???????)(v??? PP ttPtF ???? 0 0dd Impulse 冲量?? tttFI 0d ?? 0 0PPtFI tt???????? d Momentum theorem 动量定理 Not e: I ? The impulse of resultant force (2) The direction of impulse is the one changed momentum (1) Example: uniform circular motion R a 2v??A Av ?B Bv ? Amv ? Bmv ?v ?m?(3) Vector equation 0PPI ?????0 0tt ppf xxx??????相互作用时间短动量变化可观相互作用力很大(4) Impulsive force 冲击力 immitFI xx tt xx???)( 0 0vv???? djmmjtFI yy tt yy???)( 0 0vv???? dkmmktFI zz tt zz???)( 0 0vv???? d Average impulsive force 例一重锤从高度 h= 处自由落下,锤与被加工的工件碰撞后末速为零。若打击时间?t为、、 2110 10 ??试计算平均冲击力与重力的比值。 zh gh 2 0??v0? zv撞后动量定理 gh mmmt mg N t2 d)( 0 0??????vv z gh mt mg tN2????tg ht mg N?????? 55 .01 211)s(t? mg N/ 2 10 ?3 10 ?4 10 ?210 ?56 310 ?撞击作用持续时间愈短 mg N/愈大重力可略去重锤 m与工件撞击前解,s10 10 43??、 § 1 Momentum theorem for a system §系统的动量定理§? Preparatory treatment 预备知识§ system ; internal force ; external force §? Momentum theorem for a system §2 The law of Conservation of momentum 质点系统过程动量定理牛三(1) (2) (3) (t-t0) 系统的动量定理动量守恒定律条件 0?? i iF ?(4) (1) system : m1 m2 m3 1m 3m 2m 10 1v ?m 20 2v ?m 30 3v ?m 1F ?2F ? 3F ? 0tt 12f ? 21f ? 31f ? 13f ? 11v ?m 22v ?m 33v ?m 23f ? 32f ?????? tt iiiiiiiitffFmmm 0d)(: 32 0?????vv????? 31 0 31i ii im m iivv ????????????? tt tti i tfffffftF 0 0 d) )(d 23 32 31 13 21 12 31???????+ ( ) + ( (3) The third law 23 32 31 13 21 12,,ffffff ????????????????????? tti i i iitF mm 031 31 0d ??? iivv (2) Momentum theorem (4) Momentum theorem for a system ?????? i ii i tti immdtF 0 0iivv ???作用于系统的合外力的冲量等于系统动量的增量 Extens